The Silk Road website that was shut down by US authorities, who branded it a black market for drugs and other illicit wares, relied on Tor and Bitcoins to protect the anonymity of users.
The Tor network is a platform for online anonymity. The original name was The Onion Router, hence the acronym TOR, because the free software promises layers of protection.
Tor software encrypts online activities such as website visits or messages, and routes data through a worldwide network of relays that peel back only slight layers needed to pass information to subsequent points on the Internet.
Tor community members volunteer their computers to provide relay points and the resulting network makes it a challenge to trace Internet activities.
Privacy advocates tout Tor networks as a necessary option for Internet users to protect themselves from online snooping.
Bitcoins are a digital currency likened to an Internet Age version of cash. The four-year old currency is increasingly used to make payments in online transactions.
Bitcoins are created or exchanged using complex software protocols that have resulted in them being referred to as "cryptocurrency." Transactions are processed on servers called Bitcoin miners.
There is an estimated $1.5 billion in bitcoins on the market and the digital currency can be transferred directly between smartphones or any other type of computers, raising concerns by regulators it will be used for criminal or terrorist activities.
Explore further: US authorities shut Silk Road website, arrest owner (Update 2)